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quantity as the fretus grows older and after birth, the study of their 

 development in this region gives unsatisfactory results. It is definite, 

 however, that they always appear around the bundles of white fibers^ 

 being covered, especially at their points of anastomosis, with nuclei 

 and endoplasm. If the early formation of elastic tissue in the syncy- 

 tium of the walls of the umbilical artery is considered the type we 

 must interpret what has been found in the skin as a secondary differ- 

 entiation of the exoplasm, which is already collagenous, into elastic 

 tissue, as is also the case in the ground substance of the cartilage. In 

 the cartilage, however, the fibers develop in the middle of the ground 

 substance, as far away from the nuclei as possible, while in the skin the 

 elastic fibers appear at the periphery of the bundles of white fibers, 

 close to the nuclei." The same is true regarding the elastic fibers which 

 are formed in the lymph follicle along some of the reticulum fibrils. 



From this histogenetic study it must be concluded that elastic tissue 

 is a more highly differentiated tissue accolnpanying to a greater or less 

 extent all collagenous tissues (reticulum, cartilage, bone, and white 

 fibrous tissue) with the exception of the cornea. 



The study of the growth of all connective tissues is difficult, for after 

 they are once differentiated and quite sharply separated from the nuclei 

 and endoplasm they have then power of further growth and expansion 

 without a continuous transformation of endoplasm into exoplasm. 



'^ See also Jores, Ziegler's Beitrage, xxvii, Fig. 4. 



